A quadrillion tons of diamonds lie 100 miles below the earth's surface, spread across vast rock formations called "cratons," according to a study published by a team of researchers from MIT, Harvard, the University of California at Berkeley and other top-tier institutions.

The scientists made their discovery while studying the deepest parts of the Earth using sound waves. Apparently these waves move at differing speeds, depending on the temperature, density and composition of the material they travel through.

The researchers found that the sound waves moved much faster than expected when passing through the bottom of cratons, which the scientists described as underground rock formations that resemble inverted mountains.

After conducting a series of experiments to try to simulate the results in a lab, the researchers concluded that rocks containing 1-2% diamond were the only ones that could duplicate the sound wave velocities achieved in the cratons.

“It’s circumstantial evidence, but we’ve pieced it all together,” said study co-author Ulrich Faul, a research scientist in MIT's Department of Earth, Atmospheric and Planetary Sciences. “We went through all the different possibilities, from every angle, and this is the only one that’s left as a reasonable explanation.”

In the study, which was published in the June edition of the journal Geochemistry, Geophysics, Geosystems, the researchers suggested that cratonic roots are 1-2% diamond. When they did the math, that translated into a quadrillion tons of the precious gems. The number quadrillion looks like this... 1,000,000,000,000,000.

While the researchers now believe that there are 1,000 times more diamonds hidden below the Earth's surface than they previously assumed, they were quick to point out that none of the gem crystals are accessible by conventional mining methods.

Diamonds can blast to the surface during volcanic eruptions. The vertical superhighways that take the diamonds on their 100-plus mile journey are called kimberlite pipes.

Credit: Rough diamond exhibited at the Senckenberg Museum, Frankfurt, Germany. Photo by User:KS_aus_F (User:KS_aus_F) [GFDL 1.2 or FAL], via Wikimedia Commons.